1. Technical Field
This invention relates generally to elastic laminates, and more particularly to a laminate having an elastic polymer film core with at least one layer of an extensible nonwoven web bonded to each side of the elastic polymer film core.
2. Background Art
There is a recognized need for a tear resistant elastic laminate that has a soft, comfortable outer surface. For example, in personal hygiene products such as diapers, there is a need for an elastic ear that can be stretched to provide a comfortable fit for the different anatomies of various wearers, improve the fit and comfort, reduce leakage, and be compatible with adhesive and mechanical fasteners. To provide the necessary stretching characteristics, the diaper ear must be formed of an elastic material that can stretch and recover without tearing prematurely. Moreover, there is a need to provide a lightweight cloth-like film based laminate that has an elastic recovery from stretching that is comparable to natural or synthetic rubber films in the transverse direction, and has a tear resistance that is comparable to durable cotton or fabrics composed of LYRCA® synthetic fibers or filaments.
Several arrangements have been proposed for tear-resistant elastic laminates. For example, U.S. Pat. No. 5,709,921 issued Jan. 20, 1998 to Susan Elaine Shawver, discloses a multi-layer material formed of layers of elastomeric films, fibers, or webs. However, elastomeric materials, when disposed as the outer surface of a laminate, do not provide the softness and comfort characteristics of nonelastomeric outer webs. U.S. Pat. No. 5,226,992 issued Jul. 13, 1993 to Michael T. Morman, requires the use of force to pre-tension a necked non-woven prior to laminating to form a composite elastic neck-bonded laminate. This laminate is stretchable in a direction parallel to the direction of constriction or necking. It does not provide strong tear resistance due to the presence of the stressed necked material layer in the laminate. Another patent, also issued to Michael T. Morman, U.S. Pat. No. 4,981,474 on Jan. 1, 1991, discloses a composite material having a nonelastic material bonded to an elastic material while the elastic material is in a stretched condition so that when the elastic material is relaxed, the nonelastic material gathers between the locations where it is bonded to the elastic material. The resulting composite elastic material is only stretchable to the extent that the nonelastic material gathered between the bond locations allows the elastic material to elongate. Thus, in this arrangement, the elasticity of the laminate is limited by the inability of the nonelastic material to stretch beyond its initial dimensions. Moreover, the formed laminate is bulky and difficult to process. Another example of an elastic laminated sheet is disclosed in U.S. Pat. No. 5,422,172 issued Jun. 6, 1995 to Pai-Chuan Wu, which discloses an elastic laminate formed by stretching, thus compromising the tear resistance of the laminate. U.S. Pat. No. 5,354,597 issued Oct. 11, 1994 to Karen M. Capik, et al, discloses an adhesive tape having a multi-layered construction in which at least one of the layers is formed of an elastomeric material and at least one other layer that is pre-stretched beyond its elastic limit. The tape does not provide the softness or comfort provided by an externally disposed nonwoven web.
The present invention is directed to overcoming the problems set forth above. There is a demonstrated need for a laminate that has the outer softness of a nonelastomeric nonwoven web, the elasticity of an elastomeric film, and the tear resistance of a conventional packaging film. There is also a demonstrated need for such a laminate that is easy to form and economical to produce.